As is known in the art, there are various applications where an air quality or environmental air measurement system will be utilized to sense one or more indoor air quality parameters for purposes of monitoring and or providing signals for regulating environmental conditions within a building. For example, air measurement systems may be used to monitor air quality parameters including volatile organic compounds (VOCs), as well as inorganic compounds, in order to determine if parameter concentrations are within health or comfort guidelines.
It may be desirable to conduct such measurements on a continuous basis for multiple locations throughout the building or facility, especially in critical environments where specific airborne contaminants or classes of contaminant are expected to accumulate that may have undesirable affects on occupant health or comfort. In order to accomplish this, sensors have been applied using two conventional approaches to monitor the building locations of interest. This includes either the application of discrete sensors installed within each building location, or the use of a centralized monitoring approach, in which a single suite of one or more sensors is installed to sense a plurality of locations using what is generally referred to as a multipoint air sampling system. Considerations that are driving decision makers to increasingly choose multipoint air sampling approaches versus the use of discrete sensors installed within the sensed location concerns factors such as: the ease of implementation, better measurement accuracy, ease of sensor maintenance, and lower initial sensor cost as well as replacement sensor cost over the discrete sensor approach.
For one class of these multipoint air sampling systems, multiple tubes may be used to bring air samples from multiple locations to a centralized sensor(s). Centrally located air switches and/or solenoid valves may be used in this approach to sequentially switch the air from these locations through the different tubes to the sensor to measure the air from the multiple remote locations. These octopus-like systems, which are sometimes known as star-configured or home run systems, use considerable amounts of tubing, but can still be more effective than the discrete sensor approach. An example of such a star-configured system is described in U.S. Pat. No. 6,241,950, which is incorporated herein by reference.
Other types of systems known in the art of air monitoring include those that are designed to monitor refrigerants and other toxic gases, which also are star-configured systems. For example, refrigerant monitoring systems can often use a single expensive non-dispersive infrared (NDIR) sensor to cost-effectively monitor multiple locations for refrigerant leaks, which is far more cost effective than deploying a discrete NDIR sensor per monitored location. However, these sensors tend to work best when detecting parameters against toxic limit values (TLVs), given the accuracy issues that can arise due to sensor fouling.
Another multipoint sampling system known as a networked air sampling system uses a central. ‘backbone’ tube with branches extending to various locations forming a bus-configured or tree-like approach similar to the configuration of a data network. Air solenoids are typically remotely located proximate to the multiple sampling locations. Networked air sampling systems can also include remote and/or multiple-location air sampling through a tube or pipe for sampling locations in a building, outdoor air or ambient sampling, and sampling in smokestacks and exhaust air stacks. An exemplary networked air sampling system is described in U.S. Pat. No. 6,125,710, which is incorporated herein by reference.
Multipoint sampling systems may be applied to monitor a wide range of locations throughout a building, including any kinds of rooms, hallways, lobbies, interstitial spaces, penthouses, outdoor locations, and any number of locations within ductwork, plenums, and air handlers.
A sensor that may be utilized within a multipoint air sampling system includes as photoionization detector or PID, which is a sensor technology known to those experienced in the art of environmental monitoring as a device which can be used to perform a broad measurement of volatile organic compounds, as well as certain non-volatile organic compounds. PID technology may range in cost from a few hundred dollars to even several thousand dollars per sensor, yet it can be cost effective when used multipoint air sampling systems, as the cost of the sensor is divided among the number of locations sensed by the system. Conversely, PIDs are rarely applied as discrete sensors installed within each location within a building, due to initial sensor costs and maintenance. PIDs can be utilized within hand-held instruments, such as for example various models of the ppbRAE, manufactured by RAE Systems Inc., along with various models made by other manufacturers, including but not limited to: Baseline-MOCON, Inc. Photovac-Inficon, inc., RKI Instruments, etc.
Rather than provide continuous monitoring, these handheld instruments are designed to perform spot checking and general environmental survey work within a facility or, since they are portable, even in locations outside of a facility. These handheld instruments are often utilized by Environmental Health and Safety (EH&S), facilities personnel, and other facility staff, and these instruments usually have some level of data logging capability, but they do not lend themselves to being permanently installed in order to provide continuous monitoring or to provide signals for purposes of adjusting ventilation based on air quality levels. Also, the PIDs designed for handheld units generally require frequent calibration, and are therefore not practical for continuous use.
One characteristic of a photoionization detector is that it is capable of providing a signal that is simultaneously responsive to multiple compounds. This is based on the way in which these sensors provide detection of compounds, whereby the PID will respond to compounds that have an ionization potential less than or equal to that supplied by the detector's ionization source, which is usually an ultraviolet lamp. Photoionization occurs when a molecule absorbs a photon of energy at a sufficient level to release an electron to create a positive ion. This will occur when the ionization potential of the molecule in electron volts (eV) is less than the energy of the photon. As a compound is ionized by a PID lamp, electron flow is measured as an electrical current that is setup in the sensor electrode, and this current is proportional to the concentration of the gas that has been ionized. Because different compounds can be ionized at a given time, the sensor will be responsive to concentrations of multiple compounds.
Generally, the gases which may be sensed by a PID are those that have an ionization potential that is less than the ionization energy of the PID lamp. Common lamp energy levels available in PIDs include but are not limited to: 11.7 eV, 10.6 eV, 10.0 eV, and 9.6 eV. Therefore, as an example, a PID having a 10.6 eV lamp is capable of detecting acetone, which is a compound having an ionization potential (IP) of 9.69 eV yet, that PID with the same lamp will not detect chlorine, which has an IP of 11.48 eV, and therefore will not be ionized by a 10.6 eV lamp.
Because of the ability of a PID to provide a signal that is responsive to multiple compounds, it has been utilized extensively over recent years within a network air sampling system like that described by U.S. Pat. No. 6,125,710, which is also known commercially as the OptiNet system, produced by Aircuity Inc. The sensor responsiveness to many VOCs and certain no makes it quite useful as a device for providing measurements that can serve as general indications of IEQ, as well as in rendering a signal that can be used by a ventilation control system, such as that found in a laboratory, vivarium, general office space, and other environments. The application of controlling ventilation as a function of contaminant levels within a sensed space is generally known to those knowledgeable in the art of ventilation controls as Demand Control Ventilation, or DCV. As an example, U.S. Pat. No. 8,147,302 B2, which is incorporated herein by reference, describes an exemplary embodiment of how to form a DCV signal to control ventilation levels in a laboratory by way of making a differential measurement of air contaminants, and an excellent approach for making such measurements incorporates a PID sensor. In applications such as this, the broad sensing capabilities of the PID sensor is very desirable since, especially in lab environments, there are potentially hundreds of compounds that need to be detected in order to safely maintain ventilation levels as a part of the DCV strategy.
One motivation for this and other DCV methods is to reduce ventilation rates in order to realize energy savings, by reducing fan energy consumption and the costs associated with heating, cooling, and humidification of air serving the sensed environment. Energy usage relating to ventilation represents one of the most significant operating costs for commercial buildings and, increasingly DCV is being adopted as a leading initiative for facility energy retrofits. The energy efficiency opportunity associated with these programs is so significant that gas and electric utilities are regularly paying incentives to help find significant costs in these retrofits. However, ventilation reductions via DCV must be done in a manner that does not compromise the health and safety of occupants. Within research labs and other similar environments, herein referred to as critical environments, the energy savings opportunity afforded by ventilation reductions is potentially enormous, given that these types of spaces have historically been operated in a substantially over-ventilated manner. From an energy use standpoint, this is compounded by the fact that the air handling or fan systems supplying ventilation to critical spaces are usually designed as “single pass” or 100% outside air systems. This means that for every cubic foot per minute (CFM) of air supplied to these spaces, a matching CFM of outside air must be heated, cooled, or humidified. This is different from conventional recirculating air handling systems used in general commercial office buildings, which can often operate on a fraction of the outside air percentage.
Critical environments have been historically heavily overventilated due to many factors including conservative designs and initial designs which provided high ventilation rates in order to satisfy thermal loads which are now no longer present, due to the use of more energy efficient equipment, including more efficient lighting, LCD monitors instead of CRT's, and more efficient refrigerators and freezers used in these spaces. Also, today's laboratories, especially in the life sciences, operate with fewer fume hoods due to the increasing use of microchemistry, where chemicals are used in minute quantities not requiring a fume hood, and computational chemistry; and this helps to drive required ventilation rates lower. Further, AIHA/ANSI Z9.5 laboratory ventilation standards have reduced fume hood minimum flow rate recommendations for variable air volume fume hoods. In addition, the application of a DCV strategy to vary ventilation rates in these critical spaces has only been a trend over recent years given the introduction of technologies such as that described within the teachings of U.S. Pat. No. 8,147,302.
The recent trend to lower ventilation rates in critical environments, has been to reduce air change rates (ACH) in labs from previous designs having fixed values of as much as 12 or more ACH to (using DCV) levels as low as 4 ACH during occupied hours and as low as 2 ACH during unoccupied hours. Such measures can result in ventilation energy reductions by a factor of 3 or more, without compromising occupant health and safety. As mentioned previously, the use of a PID is valuable to these DCV applications, given its broad sensing capabilities, which allows it to detect most of the compounds of interest that occupants may be exposed to in the event of a chemical spill or fugitive emission. In the event of a spill, fugitive emission, or some other source of elevated contaminant levels, the multipoint sampling system monitoring the lab environment via the PID sensor will increase the ventilation or DCV signal provided to the ventilation control system, thus increasing the lab ACH in order to properly dilute the contaminant levels. Under such events, it is common for ventilation rates to be temporarily increased to 12 or more ACH, until contaminant levels in the monitored space subside.
Vivariums or animal holding rooms (also known as laboratory animal facilities, animal rooms, barrier facilities, and other names which are well known to those experienced in the art of managing facilities designed to hold animals) are another type of critical environment which use large amounts of ventilation energy. Generally, vivariums can vary in design based on the types of animals that are to be housed, which can include species of rodents, reptiles, birds, non-human primates, and even fish and other animals, but most commonly house rodents, such as rats and mice. Animal rooms are commonly found in most research facilities, including but not limited to pharmaceutical and higher education facilities, where biomedical and psychological research is conducted. In biomedical research, animals are used extensively in research and development of drugs and treatments, including discovery, safety testing, clinical trials, and even during the drug manufacturing stage. Mice and rats are often used because their immunological responses and genetic structures closely resemble that of humans, and this is very important to disease research and drug development. In fact the pharmaceutical industry is especially dependent on animal research for product development, and this has resulted in an industry where animals, such as rats and mice, are genetically bread for specific research requirements. Because of the time and effort invested into these animals and the critical role that they play in research, they can be valuable assets. As such, peat care is taken to ensure that the environment that they are housed in is a healthy one, especially in terms of IEQ, light levels, temperature, and relative humidity.
When rodents are housed, they are usually placed within individual bins or cages, and these cages are often combined within a rack comprising multiple cages. Examples of cages and cage rack systems include but are not limited to those disclosed in U.S. Pat. No. 5,865,144, U.S. Pat. No. 4,365,590, and U.S. Pat. No. 7,527,020, all of which are incorporated herein. Each cage is typically capable of containing 1 or 2 rats or up to 4 or 5 mice; and a rack, which will usually be on wheels may comprise 100 or more cages stacked in vertical and horizontal directions. Thus, the cage rack approach provides an effective way to house many animals in a relatively small space. Also, it is very common for animal holding rooms to contain numerous cages; and therefore these rooms, at any one time may contain hundreds and in some cases, thousands, of animals. A few of the more common manufacturers of these cage rack systems include: Animal Care Systems Inc., Allentown Inc., Tecniplast S.p.A., and Arrowmight, Inc. Those versed in the art of housing animals in vivarium facilities, will recognize that the cage in which the animal is housed is typically referred to as the primary space or microenvironment, while the room in which the cage or cage rack is placed is typically called the secondary space or macroenvironement.
In one known cage rack system, the individual cages within the cage rack are in communication with the secondary environment such that any gases or vapors emanating from within the cage are allowed to flow or diffuse into the secondary space. In this embodiment, the cage rack system is said to be non-ventilated, or un-ventilated. Also, non ventilated cage rack systems are in bidirectional vapor communication with the secondary space, in that, vapor contaminants in the secondary space will freely diffuse into the individual cages. In another conventional cage rack system, the individual cages within the cage rack are connected to an exhaust duct, which is used to continuously exhaust a finite amount of airflow from the cages, thus preventing vapors from the cages from flowing into the secondary space. In this embodiment, the cage rack system is said to be ventilated. There are other variations of ventilated cage racks that may include supply flow or a combination of supply and exhaust flow to the cage rack system but, the most common of the ventilated cage rack systems by far typically are those which are provided with exhaust airflow. Also, when only exhaust airflow is provided to the cage rack systems, the cages will be at a slightly negative pressure with respect to the secondary space surroundings and, thus, air will generally flow from the secondary space or environment to the cages. Therefore, regardless of whether the cage rack system is ventilated or non-ventilated, it is desirable to maintain the quality of the secondary space environment, as it can have direct impact on the health and well being of the animals in their cages.
FIG. 1 is a simplified illustration of some of the equipment and ventilation system components found within a typical animal holding room 115. Usually, especially if mice or other rodents are involved, this includes a cage rack system 111, which contains a plurality of cages 110. Each of the cages 110 provides a microenvironment to protect the animals. The cage rack system 111 can be on wheels 114 for mobility to enable the entire rack system 111 to be moved with ease for cleaning purposes as well as to enable the rack system 111 to be easily transported to another location. If the cage rack system is a ventilated one, such as that shown in FIG. 1, it typically at least includes a connection to the exhaust system 107. The exhaust system 107 is actually a plenum connection that will usually connect through manifolded ductwork to an exhaust fan that usually serves a number of rooms.
The ventilated cage rack 111 can use the macroenvironment of the animal holding room 115 as a source of makeup air, so that air flows freely from the surroundings 116 into each cage 110. Alternatively, supply air may be provided to cage rack 111 by way of a localized supply fan 108, which also usually incorporates a filter assembly. This provides airflow to supply the cages 110 through manifold 109. Exhaust air is then carried, through manifold 113 through ductwork connection 112 through airflow control device 104. Ventilation to the macroenvironment is provided via supply air 103 through airflow control device 102 via the supply air plenum 101, which is usually connected to manifolded ductwork to a supply fan that usually servers multiple rooms in the facility. Air is exhausted from room 115 via exhaust flow control device 105, which is connected to an exhaust fan through 107. In application, the pressurization of space 115 is established based on the difference between the airflow rate supplied via 102 to the space and that exhausted from the space through 105. In addition, any net airflow from the surroundings 116 supplements the exhaust quantity through 105. Therefore, if supply fan 108 is not present, the pressurization of space 115 will be determined based on the difference between the supply air provided via supply flow control device 102 and the sum of the exhaust flows provided via exhaust flow control devices 104 and 105. When the total flow exhausted from environment 116 exceeds that supplied to it (a flow condition known in the art as a negative offset), the space 116 is said to be negatively pressurized. A space that is negatively pressurizes acts to prevent contaminants from migrating beyond room 115 to other rooms or corridors that may surround this space. When a space is set to a negative offset or is negatively pressurized, airflow is allowed to flow from spaces external to room 115 via gaps under the door(s) leading to the space 115.
In other configurations, the total supply flow via 102 will be set higher than the total exhausted from environment 116, and the space 115 is said to be positively pressurized via a positive offset. In this case no air, and therefore no contaminants, will flow from the rooms or corridor external to space 115, but air will instead flow from environment 116 into these surroundings; again through gaps under the door(s) leading to the space 115. In a positively pressurized mode environment 116 will be isolated from its surroundings.
Similar to general research labs, vivariums are usually ventilated with 100% outside air, and they have historically been operated at relatively high air change rates, at levels that can be even higher than that of research labs. Here, it is not uncommon for vivariums to operate at levels of 15 to 20 ACH, or even higher levels. In many cases vivariums used to be designed to operate at sine high air change rates to ensure that worst case thermal loads could be supported due to heat generated by the animals as large numbers of animals are housed. In addition, under this circumstance, given the legacy caging systems, which generally were not ventilated, the odor levels as well as levels of toxins in a holding room could reach unacceptable levels for personnel working in those rooms. However, the increased use of ventilated cage racks has allowed air change rates in the secondary environments to be lowered significantly and, increasingly, demand control ventilation, using the teachings of U.S. Pat. No. 8,147,302 B2, is being applied to vivariums in order to realize significant reductions in energy usage. Given the enormous energy costs associated with running vivarium facilities, there is also an increasing trend to apply DCV even when non ventilated cage racks are in use.
One of the compounds of concern in vivarium applications is the ammonia that is generated as a result of the microbial decomposition of animal wastes. Ammonia concentrations from animal cages tend to increase over time as animal bedding becomes soiled. The rate at which this happens is partially a function of the type of bedding used the amount of waste produced by each animal and environmental conditions, such as relative humidity and temperature. For mice, rats, and other rodents, a variety of different beddings may be used including: hard wood chips, corn cob bedding, pine shavings, cellulose bedding, and many other types of materials, that are chosen based on tradeoffs between bedding cost, the quality of the environment required, and the longevity that a bedding can provide before it needs to be changed. The frequency with which cages need to be changed is a practical issue, as the bedding changing process tends to stress the animals, which may in turn affect their health. Regardless of the bedding used, bedding needs to be changed, and cages cleaned, on a periodic basis, and there is a definite correlation between the ammonia levels emanating from a cage and the cleanliness of the cage environment. Ammonia levels allowed to emanate from cages into the vivarium's secondary space can affect the health and well being of personnel who care for the animals and the ventilation system plays an important role in maintaining the quality of this environment. Moreover, the amount of ammonia production from a typically active unventilated cage rack can easily result in ammonia concentrations within the secondary space that exceed health limits, if that space is not sufficiently ventilated.
The National Institute for Occupational Safety and Health (NIOSH) has set the toxic limit value (TLV) for ammonia as 35 ppm, based on a time weighted average (TWA) exposure of 8 hours. Industry practice has been to keep ammonia concentrations well below the 35 ppm TWA within the vivarium secondary space, while also minimizing the frequency of bedding changes. In addition, chronic occupation exposure to ammonia at concentration even less than the prescribed TLV's has been linked to abnormal respiratory conditions including bronchial hyperresponsiveness, coughing, wheezing, and discomfort.
Before the use of continuous monitoring technologies, such as that described within the teachings of U.S. Pat. No. 6,125,710, the most common ways to provide verification of the secondary space IEQ was to use hand held sensors specific to ammonia, a handheld PID, or to perform air sampling by way of grab sample devices, such as colorimetric gas detection tubes. Those experienced in the art of environmental monitoring will recognize that a colorimetric gas detection tube (a Draeger tube, for example) is a consumable device, that is used once and then disposed of. To provide more sampled data specific to ammonia, handheld electrochemical sensors have been used and can provide fairly accurate measurements over short periods of time. Electrochemical sensors work by using an electrolyte to oxidize or reduce the target compound. The electrochemical reaction produces a current which is measured and is proportional to the concentration of the target gas. These sensors are better suited for use in a handheld device, where they can be frequently calibrated or replaced, given the practical limitations on calibration stability and the useful life of these devices. One characteristic of electrochemical sensors used to detect ammonia is that they have a life expectancy rating in ppm/hours. When exposed to low ammonia concentrations (a few ppm), they can last for many months. However, given, the relatively high levels of ammonia that will be present even in a well-ventilated vivarium, often exceeding 15 ppm, most can only continuously operate accurately for a period of a few days. This is not a problem with the way a handheld instrument is used, however, given that they will only be used for a few hours at a time and, that they can be readily recalibrated between uses.
Alternatively, IEQ verification can also be provided using a handheld PID sensor having an appropriate lamp which is able to ionize ammonia. For example, the ionization potential of ammonia is 10.16 eV so, using a PIT) with a more commonly available 10.6 eV lamp, or even one with an 11.7 eV lamp, provides an effective way to broadly measure for ammonia levels, but it will also be responsive to other compounds in the measured environment. Handheld PIDs are commonly used by EH&S and other professionals for general monitoring of IEQ conditions in any type of facility both fir purposes of routine inspection as well as in response to an event, such as a chemical spill. Because of its broad response and use in detecting many different compounds, a PID is often calibrated on one reference compound and response factors are established to that reference compound for the various compounds to be measured. These response factors do vary with the PID design along with the energy of the lamp. For example, it is common to calibrate a PID sensor on isobutylene and most manufacturers have established a list of compound response factors to this reference compound. Thus, measurements made from a PID calibrated in this way will be in units of isobutylene (often called “as isobutylene”). Using a PID with a 10.66 eV lamp, a common response factor for ammonia includes, but is not limited to, 9.4. This means that when such a PID is exposed to 9.4 ppm of ammonia, its reading will be 1 ppm as isobutylene.
As has been described above, PIDs have found use in multipoint sampling systems (such as the system disclosed in U.S. Pat. No. 8,147,302 B2 and 6,126,710) in order to provide DCV and or IEQ monitoring functions. The sensitivity that these sensors have to many different compounds can be quite beneficial, especially when measuring for a plurality of different compounds. However, the sensor's lack of specificity to certain compounds can at times result in an over response to an IEQ condition, which can represent the condition as being more serious than it really is and, can result in higher ventilation rates than is necessary, as a result of the DCV response to the IEQ condition. For example, in vivariums rats and mice are sometimes provided with softwood bedding (typically aspen shavings) which can emit low levels of beta-pinene. Beta-pinene is detected by PIDs using any of the common lamps including but not limited to: 11.7 eV, 10.6 eV, 10.0 eV, and 9.6 eV. For any of these PID lamp types, beta-pinane has a strong response due to its relatively low ionization potential of approximately 8.0 eV. For example, a typical response factor for this compound when using a 10.6 eV lamp is 0.40. That means that 0.4 ppm of beta-pinene results in a 1 ppm as isobutylene response. Given a typical response factor for ammonia, the presence 0.4 ppm of beta-pinene will appear similar to that of 9.4 ppm of ammonia. However, beta-pinene is not toxic at practical levels that may be seen in such environments yet, its presence can and does usually result in an overestimation of the IEQ levels in these environments; again depending on the type of bedding used. In vivariums, there are a number of relatively benign. “interfering” compounds which will naturally be present due to a combination of bedding materials, the use of cleaning agents, and volatile organic compounds emanating from the animal cages. This includes but is not limited to: dimethyldisulfide, acetone, and various mercaptans.